Low-latency, low-overhead data framing method for capacity-limited delay-sensitive long distance communication

ABSTRACT

A communication method is configured to increase speed of messages reception over a bandwidth limited channel such as high frequency (HF) radio. User data arriving from a high-speed network is transformed into a format suitable for transmission over the radio channel. Message packets that will take longer to reach a destination via the radio channel as compared to alternative channels, such as a fiber optic network, are rejected for radio transmission. When the packet is received, the receiver deduces message length by using information from various error handling techniques, such as forward error correction (FEC) and cyclic redundancy check (CRC) techniques. Fill data is transmitted between message packets when no data is available. The FEC and CRC information for the fill data is modified so that the fill data will fail FEC and CRC checks at the receiving station.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/767,196, filed on Nov. 14, 2018, which is herebyincorporated by reference.

BACKGROUND

Typical over the air (OTA) radio transmissions can have significantlatencies when transmitted over long distances such as across oceans.Moreover, these transmission channels can be rather noisy which in turnincreases the need for error correction. High frequency (HF) radiocommunication channels of most long-distance communication systems arelimited by the available assigned radio bandwidth and channel capacityat any given time. When using the HF radio channel in a financialhigh-frequency trading application, this limited bandwidth can causedelays in the receipt of financial instructions which in turn can befinancially detrimental.

Thus, there is a need for improvement in this field.

SUMMARY

In a radio or any communication system, there is a need to detect thestart and end of a new message so that data can be correctly decoded.The usual solutions add overhead data which reduce the fraction of theradio spectrum available for useful information. It has been found thatthis overhead adds delay and jitter.

For example, earlier methods required adding unique words to atransmitted message. Unique words are data patterns that are notexpected in data messages. Unique words are common in communicationssystems with one byte (e.g., 07EH) being a common start and end of framelimiter in packet communications. These unique words are used to tell areceiver where data is located. Placement of these unique words isusually at the beginning and/or ending of the message, but the uniquewords may be embedded in other locations of the message, or evenscattered within the message. It was found that these unique wordsconsume system capacity and add delay to the message.

Framing structures have also been proposed. In a framing structureapproach, a regular structure is transmitted with specific locations forknown data patterns (i.e., the framing overhead), system managementmessages, error correction, and user data. The amount of framingoverhead required varies with the dynamic nature of a communicationchannel. In stable systems, such as traditional time-divisionmultiplexing (TDM) telephony, the framing overhead is small. Once theframe of a TDM message is locked, the TDM message tends to stay locked.In wireless systems, due to the dynamic nature of a radio channel, asexperienced in mobile and HF systems, robust framing is required. Thisrobust framing results in a large amount of overhead in the message. Ithas been found that this fixed framing approach consumes system capacityand adds a variable delay to the message which is known as jitter. Thejitter arises as messages arrive at a system input at varying intervals.As a result, the system has to wait a variable time before a data slotis available for message transport.

With low-latency communications, it is desirable to be able to start andreceive messages as soon as possible without waiting for byte or otherframing alignment. For example, high-frequency trading as well as othertime sensitive activities needs minimal delay from end-to-end.Consequently, communications in these environments should have as littleoverhead in the transmitted message, and the message transmissionprocess should have the smallest latency or delay as possible. Packets,which may contain trading instructions, should begin transmission withminimum delay.

In light of this, a unique communication method or technique has beendeveloped to facilitate minimal, or no, transmit queuing delay, and thismethod has the capability to support asynchronous packet arrivals andtransmissions over the air. Generally speaking, this method transformsuser data arriving from a high-speed communication link into a formatsuitable for transmission over a much slower radio channel. Packettransmission time over the radio channel is typically longer than on thehigh speed link. This results in the need to reject packets at thetransmitter if the packets will be delayed by any transmit queue beyondwhat is useful for the trading application. Packets that will takelonger to reach a destination via the radio channel as compared toalternative channels, such as a high-speed fiber optic network, arerejected for transmission over the radio channel.

Fill data is generally transmitted when no user data is available fortransmission. The fill data produces an idle sequence for the radioreceiver to maintain lock onto the transmitted waveform. The fill datamay be interrupted at any time without consequence to systemperformance. However, the fill data rarely may be incorrectly identifiedat a receiving station as being a legitimate. To avoid this false packetdetection, the fill data in one example is pre-processed at thetransmission station. In one example, the transmitted message along withthe fill data are processed using forward error correction (FEC) andcyclic redundancy check (CRC) schemes. However, the FEC and CRCinformation for the fill data is modified so that the fill data willfail FEC and CRC checks at the receiving station. At the receivingstation, the FEC and CRC checks allow the receiving station to identifymessages and decode those messages.

Among other things, this technique is able to handle variableinter-packet timing issues, and at the same time, this techniqueprovides low communication delays. The method is used for detecting thestart of a message on a wireless channel with minimal overhead, latencyand jitter. This method also supports asynchronous transmissions thatare neither byte nor frame aligned. Using this method, messagetransmission may commence at any transmitted symbol boundary, becausethe fill data used during idles period can be interrupted withoutconsequence.

This encoding and decoding technique does not add overhead for framingwords. It should be appreciated that framing words reduce the utility ofthe radio channel by consuming radio spectrum. Moreover, this methodadds minimal jitter and latency as compared to systems using fixedframing structures or special symbol sets that typically need to bepre-pended to, appended to, or inserted into a data message. With thismethod, changing modulation techniques, packet lengths, and/or errorcorrection techniques does not require adjustments in a frame structure.Instead the receiver determines message boundaries solely or mostly byusing FEC and CRC. Additionally, changing modulation techniques, packetlengths, and/or error correction techniques does not require significantmessage padding in order to achieve framing alignment. The padding islimited to only that required to build any integer number of symbols.For practical modulation schemes, the number of padding bits isrelatively small. The packets can be transmitted on any symbol boundary,rather than waiting for byte, word, or frame alignment as the fill datacan be interrupted without penalty.

The system and techniques as described and illustrated herein concern anumber of unique and inventive aspects. Some, but by no means all, ofthese unique aspects are summarized below.

Aspect 1 generally concerns a method that includes receiving a messagefrom a primary communication channel at a receiving station.

Aspect 2 generally concerns the method of any previous aspect whichfurther includes detecting a message boundary of the through a paritycheck code in combination with an error correction scheme.

Aspect 3 generally concerns the method of any previous aspect in whichthe message has an integer number of modulated symbols.

Aspect 4 generally concerns the method of any previous aspect in whichthe primary communication channel includes a low bandwidth, low latencycommunication link.

Aspect 5 generally concerns the method of any previous aspect in whichthe primary communication channel includes a high frequency radiochannel.

Aspect 6 generally concerns the method of any previous aspect whichfurther includes receiving the message through a message data streamthat includes user data and fill data.

Aspect 7 generally concerns the method of any previous aspect in whichthe user data is encoded in an asynchronous manner in the message datastream.

Aspect 8 generally concerns the method of any previous aspect whichfurther includes maintaining a signal lock on the message data streamthrough the fill data.

Aspect 9 generally concerns the method of any previous aspect in whichthe fill data includes a pseudorandom binary sequence (PRBS).

Aspect 10 generally concerns the method of any previous aspect in whichthe fill data includes a version of the PRBS modified by the paritycheck code and the error correction scheme.

Aspect 11 generally concerns the method of any previous aspect whichfurther includes detecting a false message with the version of the PRBS.

Aspect 12 generally concerns the method of any previous aspect in whichthe version of the PRBS has been modified to fail a parity check codetest.

Aspect 13 generally concerns the method of any previous aspect in whichthe version of the PRBS has been modified to fail an error correctionscheme test.

Aspect 14 generally concerns the method of any previous aspect in whichthe parity check code includes a checksum.

Aspect 15 generally concerns the method of any previous aspect in whichthe parity check code includes a cyclic redundancy check (CRC).

Aspect 16 generally concerns the method of any previous aspect in whichthe error correction scheme includes forward error correction (FEC).

Aspect 17 generally concerns the method of any previous aspect in whichthe error correction scheme includes a convolution code scheme.

Aspect 18 generally concerns the method of any previous aspect in whichthe error correction scheme includes a tail-biting Viterbi decodingalgorithm.

Aspect 19 generally concerns the method of any previous aspect in whichthe error correction scheme includes a block code scheme.

Aspect 20 generally concerns the method of any previous aspect in whichthe error correction scheme includes a turbo block code scheme.

Aspect 21 generally concerns the method of any previous aspect whichfurther includes encoding a message data stream with user data and filldata.

Aspect 22 generally concerns the method of any previous aspect whichfurther includes modifying the fill data to reduce a chance of falsemessage detection.

Aspect 23 generally concerns the method of any previous aspect whichfurther includes encoding the message data stream with a parity checkcode in combination with an error correction scheme.

Aspect 24 generally concerns the method of any previous aspect whichfurther includes creating a modified version of the fill data in whichthe modified version fails a test for the parity check code.

Aspect 25 generally concerns the method of any previous aspect whichfurther includes creating a modified version of the fill data in whichthe modified version fails a test for the error correction scheme.

Aspect 26 generally concerns the method of any previous aspect whichfurther includes transmitting the message data stream from atransmission station.

Aspect 27 generally concerns the method of any previous aspect whichfurther includes receiving a user data packet from a high speed networkat a transmission station.

Aspect 28 generally concerns the method of any previous aspect whichfurther includes calculating a message transmission time for the userdata packet across a primary communication channel.

Aspect 29 generally concerns the method of any previous aspect whichfurther includes calculating an inter-message transmission time betweenuser data packets from the high speed network.

Aspect 30 generally concerns the method of any previous aspect whichfurther includes determining whether to transmit the user data packetover the primary communication channel at least based on the messagetransmission time and the inter-message transmission time.

Aspect 31 generally concerns the method of any previous aspect whichfurther includes accepting the user data packet for transmission over aprimary communication channel when a message transmission time is lessthan or equal to an inter-message transmission time.

Aspect 32 generally concerns the method of any previous aspect whichfurther includes transmitting a message including the user data acrossthe primary communication channel.

Aspect 33 generally concerns the method of any previous aspect whichfurther includes rejecting the user data packet for transmission over aprimary communication channel when a message transmission time plus itswaiting time in a queue, due to completion of transmissions in progress,will result in a message reception time for the new message exceeding anacceptable time limit.

Aspect 34 generally concerns the method of any previous aspect whichfurther includes transmitting a message including the user data across abackend communication channel.

Aspect 35 generally concerns the method of any previous aspect in whichthe user data packet concerns a transaction for a financial instrument.

Aspect 36 generally concerns a method for message start and stopboundary detection for use on a radio channel utilizing a redundancyparity check code in combination with a forward error correction (FEC)scheme where messages may arrive in an asynchronous manner with the onlyconstraint being an integer number of modulated symbols in each message.

Aspect 37 generally concerns the method of any previous aspect in whichthe parity check code is cyclic redundancy check (CRC) and the FECscheme uses a tail-biting Viterbi decoding algorithm of a convolutioncode.

Aspect 38 generally concerns the method of any previous aspect in whichthe application is for high-speed financial instrument trading.

Aspect 39 generally concerns the method of any previous aspect in whichthe error correction code is a block code.

Aspect 40 generally concerns the method of any previous aspect in whichthe error correction code is a Turbo block code.

Aspect 41 generally concerns the method of any previous aspect in whichthe period between messages is occupied with fill data, where such filldata is designed to be unlikely to cause false message detection at thereceiver.

Aspect 42 generally concerns a system for performing the method of anyprevious aspect.

Further forms, objects, features, aspects, benefits, advantages, andembodiments of the present invention will become apparent from adetailed description and drawings provided herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a communication system according to oneexample.

FIG. 2 is a diagrammatic view of a communication system according toanother example.

FIG. 3 is a side view of the FIG. 2 communication system in onevariation.

FIG. 4 is a diagrammatic view of the FIG. 2 communication system showingfurther details.

FIG. 5 is a diagrammatic view of a communication system according to afurther example.

FIG. 6 is a diagrammatic view of a transmission station.

FIG. 7 is a diagram illustrating a technique for user data packetencoding and user message transmission.

FIG. 8 is a flowchart illustrating a technique for accepting andrejecting user data packet for transmission.

FIG. 9 is a diagram of a technique for encoding the user data packet.

FIG. 10 is a diagrammatic view of a fill data generation system.

FIG. 11 is a diagram of a technique from decoding transmitted data.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

For the purpose of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the described embodiments and any further applications of theprinciples of the invention as described herein are contemplated aswould normally occur to one skilled in the art to which the inventionrelates. One embodiment of the invention is shown in great detail,although it will be apparent to those skilled in the relevant art thatsome features that are not relevant to the present invention may not beshown for the sake of clarity.

The reference numerals in the following description have been organizedto aid the reader in quickly identifying the drawings where variouscomponents are first shown. In particular, the drawing in which anelement first appears is typically indicated by the left-most digit(s)in the corresponding reference number. For example, an elementidentified by a “100” series reference numeral will likely first appearin FIG. 1, an element identified by a “200” series reference numeralwill likely first appear in FIG. 2, and so on.

FIG. 1 shows a generic version of a communication system 100 accordingto one example. As shown, the communication system 100 includes aninformation source 105 and an information destination 110. Theinformation source 105 and information destination 110 operativelycommunicate with one another through one or more communication channels115. Communication over these communication channels 115 can be one-waytype communications and/or two-way type communications. In theillustrated example, the communication channels 115 between theinformation source 105 and information destination 110 include a primarycommunication channel 120 and a backend communication channel 125. Inother examples, the communication system 100 can include just a singlecommunication channel 115 or more than two communication channels 115.

As will be explained in further detail below, the communication system100 can be used in a number of situations, especially in situationswhere the information source 105 and information destination 110 arelocated physically remote from one another. The communication system 100for instance can be used for private, commercial, medical, military,and/or governmental purposes. For the purposes of explanation, thecommunication system 100 will be described for use with a financialtrading system, but it should be recognized that the communicationsystem 100 can be adapted for other uses such as for issuing militarycommands and performing remote telemedicine procedures. In this example,the information source 105 and information destination 110 generallyrepresent the locations of the computer systems for remotely locatedstock/commodity exchanges and/or financial institutions that trade onthose exchanges. Some examples of these exchanges include the New YorkStock Exchange (NYSE), the NASDAQ Stock Market, Tokyo Stock Exchange(TYO), the Shanghai Stock Exchange, the Hong Kong Stock Exchange,Euronext, London Stock Exchange, Shenzhen Stock Exchange, Toronto StockExchange, Bombay Stock Exchange, Chicago Mercantile Exchange (CME),Chicago Board of Trade (CBOT), and the New York Mercantile Exchange(NYMEX), just to name a few.

As shown in FIG. 1, the information source 105 and informationdestination 110 are physically separated by a distance (“D”) 130. Forinstance, the exchanges represented by the information source 105 andinformation destination 110 can be separated by mountains, continents,and even oceans. This physical distance 130 creates a delay or latencyin communications between the information source 105 and informationdestination 110 locations. Normally, but not always, the greater thedistance 130, the longer the latency for a given communication channel115. In most cases, the distance 130 between these exchanges preventsdirect line of sight communications which further increases latency aswell as increases the risk for communication errors. For instance, theinformation destination 110 can be located past the radio horizon forthe information source 105. With trading as well as other activities,time and communication accuracy are crucial. Any delays can causetraders to lose money, and likewise, any communication errors can causea loss. Communication errors can be reduced but usually at the cost ofhigher latency and/or greater bandwidth requirements. Most communicationchannels 115 have limited bandwidth to some degree. The latency andbandwidth capabilities can vary depending on the construction and typeof communication channel 115.

As can be seen, the primary communication channel 120 has a primarychannel latency (ΔT_(P)) 135 and a primary channel bandwidth (B_(P))140. The backend channel latency 145 primary communication channel 120has a backend channel latency (ΔT_(B)) 145 and a backend channelbandwidth (B_(B)) 150. The communication channels 115 in FIG. 1 can havethe same latency and bandwidth properties or different latency and/orbandwidth as well as other properties. In one example, the primarychannel latency 135 of the primary communication channel 120 is lessthan the backend channel latency 145 of the backend communicationchannel 125, and the primary channel bandwidth 140 of the primarycommunication channel 120 is less than the backend channel bandwidth 150of the backend communication channel 125. In some variations of thisexample, the primary communication channel 120 is a wirelesscommunication channel (e.g., radio), and the backend communicationchannel 125 is a wired type communication channel (e.g., fiber opticcable). In one particular form, the primary communication channel 120uses a skywave communication technique, and the backend communicationchannel 125 includes a non-skywave path such as a fiber optic cable. Inother examples, the primary communication channel 120 and backendcommunication channel 125 represent different communication channels 115for the same type of communication mode. For instance, primarycommunication channel 120 and backend communication channel 125represent wireless communication channels having different frequencybands, and in one example, both communication channels 115 utilize highfrequency (HF) radio to communicate via skywave propagation. With theprimary communication channel 120 and backend communication channel 125having different frequencies, the primary communication channel 120 andbackend communication channel 125 can have different latencies,bandwidths, and/or communication error rates. For instance, the primarycommunication channel 120 in one situation can be noisier than thebackend communication channel 125, but the primary communication channel120 can have a shorter latency than the backend communication channel125.

The HF radio communication channel 115 of the communication system 100can be limited by the available assigned radio bandwidth and channelcapacity at any given time. When using the HF radio communicationchannel 115 in a financial high frequency trading application,increasing the number and/or transmission speed of messages increasesthe profit potential of the communication system 100. As will be furtherexplained below, a unique method has been developed to reduce thelatency of messages sent over a bandwidth-limited wireless communicationchannel 115. In addition to decreasing latency, the reduced overhead ofthis technique results in a higher number of transactions per unit oftime can be communicated and/or executed.

FIG. 2 illustrates a specific example of a communication system 200 ofthe FIG. 1 communication system 100 configured to transfer dataaccording to the unique technique described herein. Like in the FIG. 1communication system 100, the communication system 200 in FIG. 2includes the information source 105, information destination 110, andcommunication channels 115 that include the primary communicationchannel 120 and backend communication channel 125. Specifically, thecommunication system 200 in FIG. 2 is configured to transfer data via alow latency, low bandwidth communication link 204. In one form, the lowlatency, low bandwidth communication link 204 includes a high frequencyradio channel (“HF radio”) 206. The communication system 200 in FIG. 2is further configured to transfer data via a separate data via a highlatency, high bandwidth communication link 208. The low latency, lowbandwidth communication link 204 and high latency, high bandwidthcommunication link 208 provide separate connections between a firstcommunication node 212 at a transmission station 214 and a secondcommunication node 216 at a receiving station 218. The low latency, lowbandwidth communication link 204 may be configured to transmit datausing electromagnetic waves 224 passing through free space via skywavepropagation between a transmitting antenna 228 and a receiving antenna232. The electromagnetic waves 224 may be generated by a transmitter inthe first communication node 212, passed along a transmission line 236to the transmitting antenna 228. The electromagnetic waves 224 may beradiated by the transmitting antenna 228 encountering an ionized portionof the atmosphere 220. This radiated electromagnetic energy may then berefracted by the ionized portion of the atmosphere 220 causing theelectromagnetic waves 224 to redirect toward the earth 256. Theelectromagnetic waves 224 may be received by the receiving antenna 232coupled to the second communication node 216 by the transmission line240. As illustrated in FIG. 2, a transmitting communication node may useskywave propagation to transmit electromagnetic energy long distancesacross the surface of the earth 256 without the need of one or moretransmission lines 236 to carry the electromagnetic energy.

Data may also be transmitted between the transmission station 214 andreceiving station 218 using the high latency, high bandwidthcommunication link 208. As illustrated in FIG. 2, the high latency, highbandwidth communication link 208 may be implemented using a transmissionline 244 passing through the earth 256, which may include passing underor through an ocean or other body of water. As shown in FIG. 2, the highlatency, high bandwidth communication link 208 may include one or morerepeaters 252. FIG. 2 illustrates four repeaters 252 along thetransmission line 244 although any suitable number of repeaters 252 maybe used. The transmission line 244 may also have no repeaters 252 atall. Although FIG. 2 illustrates the low latency, low bandwidthcommunication link 204 transmitting information from the firstcommunication node 212 to the second communication node 216, the datatransmitted may pass along the low latency, low bandwidth communicationlink 204 and high latency, high bandwidth communication link 208 in bothdirections.

As shown, the communication system 200 further includes a client 260that has a connection 264 to the first communication node 212. Theclient 260 is configured to send instructions over the connection 264 tothe first communication node 212. In the illustrated example, theconnection 264 includes a wireless connection 266 such as a microwavenetwork. At the first communication node 212, the instructions areprepared to be sent to the second communication node 216, either by thelow latency, low bandwidth communication link 204 or the high latency,high bandwidth communication link 208, or both. As shown, the secondcommunication node 216 is connected to an instruction processor 268 viaa connection 272. It should be recognized that the connection 272 caninclude wireless connection 266 like a microwave or other type ofwireless connection. The client 260 may be any business, group,individual, and/or entity that desires to send directions over adistance. The instruction processor 268 may be any business, group,individual, and/or entity that is meant to receive or act upon thoseinstructions. In some embodiments, the connection 264 and connection 272may be unnecessary as the client 260 may send the data to be transmitteddirectly from the first communication node 212 or the secondcommunication node 216 may be connected directly to the instructionprocessor 268. The communication system 200 may be used for any kind oflow-latency data transmission that is desired. As one example, theclient 260 may be a doctor or surgeon working remotely while theinstruction processor 268 may be a robotic instrument for working on apatient.

In some embodiments, the client 260 may be a financial instrument traderand the instruction processor 268 may be a stock exchange. The tradermay wish to provide instructions to the stock exchange to buy or sellcertain securities or bonds at specific times. Alternatively oradditionally, the instructions are in the form of news and/or otherinformation supplied by the trader and/or a third party organization,such as a news organization or a government. The trader may transmit theinstructions to the first communication node 212 which sends theinstructions and/or news to the second communication node 216 using thetransmitting antenna 228, receiving antenna 232, and/or by thetransmission line 244. The stock exchange can then process the actionsdesired by the trader upon receipt of the instructions and/or news.

The communication system 200 may be useful for high-frequency trading,where trading strategies are carried out on computers to execute tradesin fractions of a second. In high-frequency trading, a delay of meremilliseconds may cost a trader millions of dollars; therefore, the speedof transmission of trading instructions is as important as the accuracyof the data transmitted. In some embodiments, the trader may transmitpreset trading instructions or conditions for executing a trade to thesecond communication node 216, which is located within close proximityto a stock exchange, using the high latency, high bandwidthcommunication link 208 at a time before the trader wishes to execute atrade. These instructions or conditions may require the transmission ofa large amount of data, and may be delivered more accurately using thehigh latency, high bandwidth communication link 208. Also, if theinstructions or conditions are sent at a time prior to when a trade iswished to be executed, the higher latency of the high latency, highbandwidth communication link 208 can be tolerated.

The eventual execution of the instructions may be accomplished by thetrader transmitting triggering data to the communication system 200 onwhich the instructions are stored. Alternatively or additionally, thetriggering data can includes news and/or other information supplied bythe trader and/or a separate, third party organization. Upon receipt ofthe triggering data, the trading instructions are sent to the stockexchange and a trade is executed. The triggering data that istransmitted is generally a much smaller amount of data than theinstructions; therefore, the triggering data may be sent over the lowlatency, low bandwidth communication link 204. When the triggering datais received at the second communication node 216, the instructions for aspecific trade are sent to the stock exchange. Sending the triggeringdata over the low latency, low bandwidth communication link 204 ratherthan the high latency, high bandwidth communication link 208 allows thedesired trade to be executed as quickly as possible, giving the trader atime advantage over other parties trading the same financialinstruments.

The configuration shown in FIG. 2 is further illustrated in FIG. 3 wherethe first communication node 212 and the second communication node 216are geographically remote from one another separated by a substantialportion of the surface of the earth 256. This portion of the earth'ssurface may include one or more continents, oceans, mountain ranges,and/or other geographic areas. For example, the distance spanned in FIG.2 may cover a single continent, multiple continents, an ocean, and thelike. In one example, the first communication node 212 is in Chicago,Ill. in the United States of America, and the second communication node216 is in London, England, in the United Kingdom. In another example,the first communication node 212 is in New York City, N.Y., and thesecond communication node 216 is in Los Angeles, Calif., both citiesbeing in North America. As shown, the transmitting antenna 228 andreceiving antenna 232 are separated by a distance greater than the radiohorizon such that no line of sight communications can be made. Instead,a skywave communication technique is used in which the electromagneticwaves 224 of the low latency, low bandwidth communication link 204 areskipped multiple times between the transmitting antenna 228 andreceiving antenna 232. Any suitable combination of distance,communication nodes, and communications links is envisioned that canprovide satisfactory latency and bandwidth.

FIG. 2 illustrates that skywave propagation allows electromagneticenergy to traverse long distances. Using skywave propagation, the lowlatency, low bandwidth communication link 204 transmits theelectromagnetic waves 224 into a portion of the atmosphere 220 that issufficiently ionized to refract the electromagnetic waves 224 toward theearth 256. The waves may then be reflected by the surface of the earth256 and returned to the ionized portion of the upper atmosphere 220where they may be refracted toward earth 256 again. Thus electromagneticenergy may “skip” repeatedly allowing the electromagnetic waves 224 tocover distances substantially greater than those which may be covered bynon-skywave propagation.

FIG. 4 shows a specific implementation of the FIG. 2 communicationsystem 200. As can be seen, the first communication node 212 at thetransmission station 214 in FIG. 4 includes a modulator 405, a radiotransmitter 410, and a fiber optic transmitter 415. The modulator 405includes one or more processors and memory along with other electronics,software, and/or firmware configured to modulate the message and/orother information using the above-mentioned variable messaging lengthtechnique which will be further described below. The radio transmitter410 is operatively connected to the modulator 405 so as to transmit themessage and/or other data to the receiving station 218 via thetransmitting antenna 228 over the HF radio channel 206. In the depictedexample, the radio transmitter 410 transmits the message and/or otherdata via the primary communication channel 120. The fiber optictransmitter 415 is operatively connected to the modulator 405 and afiber optic cable 420 that forms at least part of the backendcommunication channel 125. The fiber optic transmitter 415 is configuredto transmit to the second communication node 216 one or more messagetables and/or other information, such as a duplicate copy of the messagetransmitted by the radio transmitter 410, via the backend communicationchannel 125.

The second communication node 216 in FIG. 4 includes a demodulator 425,a radio receiver 430, and a fiber optic receiver 435. The demodulator425 includes one or more processors and memory along with otherelectronics, software, and/or firmware configured to demodulate themessage and/or other information from the first communication node 212using the above-mentioned technique which will be further describedbelow. The radio receiver 430 is operatively connected to thedemodulator 425 so as to receive the message and/or other data from thefirst communication node 212 via the receiving antenna 232. In theillustrated example, the radio receiver 430 again receives the messageand/or other data via the primary communication channel 120. The fiberoptic receiver 435 is operatively connected to the demodulator 425 andthe fiber optic cable 420. The fiber optic receiver 435 is configured toreceive from the fiber optic transmitter 415 of the first communicationnode 212 the message tables and/or other information, such as aduplicate copy of the message from the modulator 405.

It should be recognized that the communication system 200 in FIG. 4 canfacilitate one-way communication or two-way communication. For example,the modulator 405 can be configured to act as a modulator-demodulator(modem), and the demodulator 425 can likewise be a modem. The HF radiotransmitter 410 in certain variations can be configured to receivewireless communications so as to act as a wireless transceiver.Similarly, the HF radio receiver 430 can also be a wireless transceiver.Both the fiber optic transmitter 415 and fiber optic receiver 435 can befiber optic transceivers to facilitate two-way communication.

FIG. 5 shows another variation of the communication system 100 in FIG. 1that can perform the low latency framing technique described herein. Ascan be seen, a communication system 500 in FIG. 5 is constructed in asimilar fashion and shares a number of components in common with thecommunication system 200 of FIGS. 2, 3, and 4. For instance, thecommunication system 500 includes the modulator 405 and the radiotransmitter 410 with the transmitting antenna 228 at the transmissionstation 214 of the type described before. Moreover, the communicationsystem 500 includes the demodulator 425 and the radio receiver 430 withthe receiving antenna 232 at the receiving station 218 of the kindmentioned above. As can be seen, however, the fiber optic transmitter415, fiber optic cable 420, and fiber optic receiver 435 have beeneliminated such that all communications are wireless, and moreparticularly, through skywave communication via the HF radio channel206. In one variation, the communication system 500 includes a singlecommunication channel 115 in the form of the low latency, low bandwidthcommunication link 204 that forms the primary communication channel 120.In another variation, the radio communication between the radiotransmitter 410 and radio receiver 430 is through two or more HFcommunication channels 115 such that one forms the primary communicationchannel 120 and the other forms the backend communication channel 125.In one version, the primary communication channel 120 and the backendcommunication channel 125 can have generally the same data bandwidthand/or latency, and in other versions, the primary communication channel120 and backend communication channel 125 can have different databandwidths and/or latencies. The modulator 405 in the illustratedexample is connected to the client 260 through a high speed transmitterdata network 505. The demodulator 425 is connected to the instructionprocessor 268 through a high speed receiver data network 510. In oneform, the high speed transmitter data network 505 and high speedreceiver data network 510 are high speed data networks.

FIG. 6 shows one example of a transmitter system 600 that can beimplemented in the FIG. 2 communication system 200 and the FIG. 5communication system 500 as well as other communication systems 100. Thetransmitter system 600 includes the modulator 405 and radio transmitter410 with the transmitting antenna 228 at the transmission station 214.As illustrated, the transmitter system 600 communicates with a highfrequency trading network 605 over the high speed transmitter datanetwork 505. Over the high speed transmitter data network 505, the highfrequency trading network 605 communicates user data 610, such as afinancial transaction command (e.g., buy, sell, hold, etc.), to themodulator 405 of the transmitter system 600. The high frequency tradingnetwork 605 sends the user data 610 to the transmitter system 600 withthe intent for the user data 610 to be transmitted to a receivingstation. While most of these messages are transmitted, some of thesemessages may not be ultimately transmitted to the radio receiver 430.The modulator 405 is configured to send transmission acknowledgementdata 615 over the high speed transmitter data network 505 back to thehigh frequency trading network 605 so as to acknowledge whether or notthe message was transmitted. Additional information, such as why themessage was not sent, can be further included in the transmissionacknowledgement data 615 back to the user or message requestor. Whenuser data 610 is able to be transmitted, the modulator 405 modulates theuser data 610 into transmitted data 620 which is sent to the radiotransmitter 410 for transmission.

High-frequency trading as well as other time sensitive activities needsminimal delay from end-to-end. Consequently, communications in theseenvironments should have as little overhead in the transmitted message,and the message transmission process should have the smallest latency ordelay as possible. Packets, which may contain trading instructions,should begin transmission with minimum delay. In light of this, a uniquecommunication method or technique has been developed to facilitateminimal, or no, transmit queuing delay, and this method has thecapability to support asynchronous packet arrivals and transmissionsover the air. Among other things, this technique is able to handlevariable inter-packet timing issues, and at the same time, thistechnique provides low communication delays.

As should be appreciated, the transmission time using the low latency,low bandwidth communication link 204, such as the HF radio channel 206using skywave propagation, for a given message is typically longer thanthe transmission time using the high speed transmitter data network 505.In other words, the low latency, low bandwidth communication link 204has a transmission time that is greater than the high speed transmitterdata network 505 used by the high frequency trading network 605. As aresult, the low latency, low bandwidth communication link 204 creates abottleneck along the communication path for the message. This method andsystem is configured to reduce the system-wide transmission time. In thecommunication system 200 of FIG. 2 for example, the system-widetransmission time would be generally the time a packet takes to traversethe communication system 200 from the client 260 to the instructionprocessor 268. For the communication system 500 in FIG. 5, thesystem-wide transmission time would be generally the time a packet takesto traverse the communication system 500 from the high speed transmitterdata network 505 to the high speed receiver data network 510.

FIG. 7 includes a diagram 700 that shows the relative size and timing ofthe user data 610 and transmitted data 620. In the diagram 700 of FIG.7, time 705 flows from right to left. The user data 610 includes one ormore user data packets 710. The transmitted data 620 includes one ormore user messages 715 that are created based on the user data packets710. The transmitted data 620 further includes fill data 720 that isnormally (but not always) located between the individual user messages715 so as to fill the space in between the user messages 715. Amongother things, the fill data 720 helps radio receiver 430 to maintain alock on the HF radio channel 206. The user data packets 710 aretransmitted with a high speed network packet transmission time (T_(HS))725 over the high speed transmitter data network 505. Considering the HFradio channel 206 is slower than the high speed transmitter data network505, the message time for the user data packets 710 expands on the HFradio channel 206. The modulator 405 encodes and modulates therelatively short user data packets 710 to the relatively longer usermessages 715 for the HF radio channel 206. As shown, the user messages715 each have a radio frequency channel message transmission time(T_(RF)) 730 that is longer than high speed network packet transmissiontime 725. In other words, the packet transmission time over HF radiochannel 206 is longer than the high speed network packet transmissiontime 725 on the high speed transmitter data network 505.

Each of the user messages 715 has an inter-packet period orinter-message transmission time (T_(IM)) 735 that defines the timebetween the user data packets 710. In some cases, the inter-messagetransmission time 735 is a fixed period, and the inter-messagetransmission time 735 in other cases can vary from user data packet 710to user data packet 710. In other words, the packets may be contiguousor have a variable inter-packet period. As noted before, thecommunication system 100 includes the primary communication channel 120and the backend communication channel 125. In one example, the primarycommunication channel 120 normally has low latency, but the primarycommunication channel 120 further has lower bandwidth. The backendcommunication channel 125 can have higher bandwidth than the primarycommunication channel 120, but the backend communication channel 125also has higher latency than the primary communication channel 120. Inthe FIG. 4 example, the primary communication channel 120 is the lowlatency, low bandwidth communication link 204 in the form of the HFradio channel 206, and the backend communication channel 125 is the highlatency, high bandwidth communication link 208 in the form of the fiberoptic cable 420. In the FIG. 5 example, the primary communicationchannel 120 is a first HF radio channel 206 that forms the low latency,low bandwidth communication link 204, and the backend communicationchannel 125 is a second HF radio channel 206 that forms the highlatency, high bandwidth communication link 208. Considering the primarycommunication channel 120 has a lower latency than the backendcommunication channel 125 in this example, relatively small or shortuser messages 715 that are transmitted at the same time from thetransmission station 214 along the primary communication channel 120 andbackend communication channel 125 will be first received at thereceiving station 218 via the primary communication channel 120.However, since the backend communication channel 125 has a largerbandwidth, larger user messages 715 will be received at the receivingstation 218 more quickly through the backend communication channel 125than through the primary communication channel 120. The inter-messagetransmission time 735 represents a cut-off time or value of where theprimary communication channel 120 or backend communication channel 125will be faster. Again, the cut-off time represented by the inter-messagetransmission time 735 can vary due to a number of factors, such as theconditions of the primary communication channel 120 and backendcommunication channel 125.

With this communication method, when the calculated radio frequencychannel message transmission time 730 for an individual user message 715is less than or equal to the inter-message transmission time 735, theuser message 715 is transmitted via the primary communication channel120 (e.g., the HF radio channel 206 in FIGS. 4 and 5), and when thecalculated radio frequency channel message transmission time 730 isgreater than the inter-message transmission time 735, the user message715 is transmitted to the receiving station 218 via the backendcommunication channel 125. In other words, packets at the input of theradio transmitter 410 (and/or modulator 405) in one variation arerejected if the packets will be delayed by any transmit queue beyondwhat is useful for a financial trading application or strategy. Thepackets, which will take longer to reach the receiving station 218 thanalternative communication channels 115, for example a high-speed fiberoptic network, are rejected for transmission over the HF radio channel206, and instead, the packets are sent via one or more of the fastercommunication channels 115. For instance, with the communication system200 in FIG. 4, if the user message 715 will be transmitted faster viathe HF radio channel 206, then the radio transmitter 410 transmits theuser message 715 over the HF radio channel 206 to the receiving station218. On the other hand, when the radio frequency channel messagetransmission time 730 for the user message 715 is greater than theinter-message transmission time 735, the user message 715 is transmittedvia the fiber optic cable 420 to the receiving station 218. In case of atie, one of these communication channel 115 is picked as the default, orthe user message 715 is transmitted on both the HF radio channel 206 andthe fiber optic cable 420. Sometimes duplicate copies of the usermessage 715 are also transmitted on both the HF radio channel 206 andthe fiber optic cable 420 for modem management and/or other purposes.For the FIG. 5 example, multiple HF radio channels 206 with differinglatencies and bandwidths are used to communicate the radio frequencychannel message transmission time 730 to the receiving station 218. Asimilar method is used to select the appropriate HF radio channel 206.

FIG. 8 includes a flowchart 800 illustrating this unique method ortechnique. This method will be described as the modulator 405 performingthe acts, but it should be recognized that other equipment such asseparate computers can partially or fully perform these acts. In oneform, the modulator 405 is hardwired with electronics to perform thismethod, and in other examples, the modulator 405 includes a combinationof hardware, such as a processor and memory, and software to perform theacts. In one form, the modulator 405 is incorporated into a modem thatis configured for two-way communication.

Looking at FIGS. 6, 7, and 8, the modulator 405 in stage 805 determinesif a new user data packet 710 has arrived from the high frequencytrading network 605 via the high speed transmitter data network 505. Ifa new user data packet 710 has not arrived, the modulator 405 sends afill symbol that forms the fill data 720 of the transmitted data 620that is transmitted by the radio transmitter 410. Once the fill symbolis sent, the modulator 405 then again checks if a new user data packet710 has arrived. The fill data 720 is configured to produce an idlesequence for the radio receiver 430 and the receiving station 218 tomaintain lock onto the transmitted waveform. In one example, the filldata 720 may be interrupted at any time without consequence to systemperformance.

When a new user data packet 710 arrives from the high frequency tradingnetwork 605, the modulator 405 determines whether the radio transmitter410 is transmitting transmitted data 620 with one or more user messages715 in stage 810. If the transmitted data 620 for the radio transmitter410 includes a user message 715 in stage 810, the modulator 405 in stage815 calculates, retrieves from memory, and/or otherwise determines theradio frequency channel message transmission time 730 and theinter-message transmission time 735. When the modulator 405 determinesthe inter-message transmission time 735 is more than the inter-messagetransmission time 735 in stage 820, the modulator 405 sends atransmission acknowledgement data 615 back to the high frequency tradingnetwork 605 indicating the new user data packet 710 has been rejected.When this occurs, the modulator 405 determines that the user message 715in the transmitted data 620 will collide or overlap with one another.Under this condition, the new user message 715 will not be able to beincorporated into the transmitted data 620 for transmission over the HFradio channel 206 or other primary communication channel 120. Uponreceipt of the transmission acknowledgement data 615 with this alert,the client can then take corrective action such as transmitting the userdata packets 710 over another communications channel, such as thebackend communication channel 125. Alternatively or additionally, themodulator 405 can transmit the user data packet 710 over a differentbackend communication channel 125. For instance, the modulator 405 cansend a packet with the user data packets 710 over the fiber optic cable420 (FIG. 4) and/or over a different HF radio channel 206 (FIG. 5).After rejecting the packet, the modulator 405 can proceed in continueprocessing the current in stage 825 or to stage 805.

When the new user data packet 710 passes the time limit in stage 820,the modulator 405 will process the user data packet 710 to incorporatethe requisite overhead for transmitting the transmitted data 620 via theradio transmitter 410. For example, the user message 715 in one exampleis encoded using a forward error correction (FEC) that further includesa checksum. Once the modulator 405 finishes processing the packetinformation for the user message 715 in stage 825, the modulator 405replaces the packets for the fill data 720 in the transmitted data 620with the packets for the processed user messages 715. Subsequently, theradio transmitter 410 transmits the transmitted data 620 from themodulator 405 over the HF radio channel 206 to the receiving station218. After stage 830, the modulator 405 cycles back to stage 805 so asto further monitor packet arrival of user data 610 from the highfrequency trading network 605.

FIG. 9 includes a diagram 900 that depicts an example method forperforming packet transmission processing and fill data replacement instage 825 and stage 830 of FIG. 8. Through the technique shown in thediagram 900 of FIG. 9, the modulator 405 converts the user data packet710 to the transmitted data 620. In stage 905, the modulator 405receives, retrieves, or is otherwise provided the user data packet 710.When the user data 610 arrives, the user data packet 710 is collected.The user data path is generally a high-bandwidth channel (e.g., highspeed transmitter data network 505) and data collection time is short ascompared to the radio transmission time over the HF radio channel 206.

The modulator 405 in stage 910 strips overhead data from the user datapacket 710. Unneeded packet overhead is removed in stage 910. Forexample, internet protocol (IP) header data can often be removed and/orreduced through compression techniques such as robust header compression(ROHC) developed by the Internet Engineering Task Force (IETF). In stage915, the modulator 405 adds a checksum to the data. In one example, thechecksum is a cyclic redundancy check (CRC). Other robust checksumapproaches may be used in further examples.

To promote error detection and correction at the receiving station 218,the modulator 405 in stage 920 adds FEC redundancy to enable FEC at thereceiving station 218. In one example, a tail-biting convolutional codeis used, and in another example, a Reed Solomon and/or other blockcoding scheme is used in stage 920. If needed, the modulator 405 addssymbol padding to the packet data in stage 925. This padding is used toalign the data with the OTA modulation symbol that encodes two or morebits per symbol. In stage 930, the modulator 405 converts the data intosymbols that are suitable for transmission such as via the HF radiochannel 206. The resulting transmit data that forms the transmitted data620 is generated by the modulator 405 in stage 935. In anothervariation, the packets for the fill data 720 for stage 830 in FIG. 8 areadded to the data during or after stage 935. In other words, if no userdata 610 is present, then fill data 720 is transmitted in place of theuser data 610.

Once more, fill data 720 is generally transmitted when no user data isavailable for transmission. The fill data 720 produces an idle sequencefor the radio receiver 430 to maintain lock onto the transmittedwaveform. The fill data 720 may be interrupted at any time withoutconsequence to system performance. One example of a suitable fill datatype is pseudo-noise data patterns generated with a shift registermethod. However, the fill data 720 rarely may incorrectly identified atthe receiving station 218 as being a legitimate user message 715. Asshould be appreciated, this type of false positive can be especiallydetrimental in financial transactions by causing unexpected andsignificant financial losses. To avoid this false packet detection, thefill data 720 in one example is pre-processed at the transmissionstation 214 with receive FEC and receive CRC processes.

This FEC and CRC preprocessing is used by the receiving station 218 todetect any unintended false positives. Referring again to FIG. 7, thepackets for the radio frequency channel message transmission time 730may be contiguous or have a variable inter-message transmission time735. Between the packets for the radio frequency channel messagetransmission time 730, the modulator 405 sends the fill data 720. It issometimes desirable the fill data 720 has no direct current (“DC”) bias,minimal (or no) spectral components, and/or occupies the assignedspectrum so as to optimize channel equalization.

In one example, the fill data 720 includes a pseudorandom binarysequence (“PRBS”) of data. Looking at FIG. 10, a fill data generationsystem 1000 includes a PRBS source 1005, a receive FEC decoder 1010, anda receive CRC detector 1015. It should be recognized that the fill datageneration system 1000 can implemented through hardware, software, orboth. The PRBS source 1005 is configured to generate the PRBS. The PRBSsource 1005 simulates the process of FEC decoding at the demodulator 425at the receiving station 218 based on the PRBS data. Based on the FECdata from the receive FEC decoder 1010, the PRBS source 1005 simulatesthe process of CRC detection at the demodulator 425. One or more bits orsymbols of the resulting data from the receive CRC detector 1015 can bechanged or otherwise used to modify the PRBS data such that theresulting fill data 720 will fail the FEC and CRC checks at thereceiving station 218 with minimal impact to the transmitted data 620.

FIG. 11 shows a diagram 1100 that depicts a process the demodulator 425performs to decode and detect valid messages. In stage 1105, the radioreceiver 430 converts the received RF energy from the HF radio channel206 into a digital baseband data stream. This data stream may includehard and/or soft-decision symbol estimates. The usual receiver functionsof symbol timing recovery, frequency correction, gain control, and thelike operate on both fill the user message 715 and fill data 720 asreceived. The one or more newly received symbols are appended to theolder symbols stored in the memory of the radio receiver 430. Thedecoder length, N, is of suitable length for the number of symbols in anencoded user data packet 710. The decoder length varies by messagelength, modulation selected (QPSK, 16 QAM, etc.), and the FEC overheadselected. Each is selected according to the HF channel behavior and thedesired level of error protection.

The radio receiver 430 in stage 1110 converts these received symbols inthe memory buffer to digital data so as to facilitate later decoding.The radio receiver 430 at the receiving station 218 in stage 1115 runsan FEC algorithm to decode the message and remove any FEC overhead suchas extraneous parity check bits. In this case, the FEC is done based onthe specified message length for the demodulator 425. In one example,this FEC algorithm is a Tail-Biting Viterbi Algorithm, but in otherexamples, the FEC algorithm can be a different tail-biting convolutionaldecoding algorithm and/or an FEC block code algorithm such as ReedSolomon.

The demodulator 425 in stage 1120 performs a CRC check based on the FECdecoded data to see if the message is valid. In one form, a combinationTail-Biting Viterbi FEC and a CRC checksum is used. Other FEC codes andchecksums may be used. If the CRC is not valid in stage 1120, thedemodulator 425 proceeds to wait for the next symbol in stage 1105, andthe cycle continues again. On the other hand, when a valid message isdetected in stage 1120, the radio receiver 430 strips any CRC bits fromthe message in stage 1125. If the hardware and/or software of the radioreceiver 430 used to implement stage 1115 and stage 1120 takes longerthan one symbol period to perform, then a set of multiple (M) radioreceivers 430 are used with each offset by one symbol period so that thetime to receive the encoded user message, Nx Tsymbol, divided by the Mis ≤the maximum acceptable decoder processing time.

Following stage 1125, the now stripped message is repackaged with packetoverhead and user data is added to the packet in stage 1130. Thedemodulator 425 sends a data detect signal and the decoded message tothe instruction processor 268. This new message can then be used toexecute an action such as a financial transaction.

This encoding and decoding technique does not add overhead for framingwords. It should be appreciated that framing words reduce the utility ofthe radio channel by consuming radio spectrum. Moreover, this methodadds minimal jitter and latency as compared to systems using fixedframing structures or special symbol sets that typically need to bepre-pended to, appended to, or inserted into a data message. With thismethod, changing modulation techniques, packet lengths, and/or errorcorrection techniques does not require adjustments in a frame structure.Instead the receiver determines message boundaries solely or mostly byusing FEC and CRC. Additionally, changing modulation techniques, packetlengths, and/or error correction techniques does not require significantmessage padding in order to achieve framing alignment. The padding islimited to only that required to build any integer number of symbols.For practical modulation schemes, the number of padding bits isrelatively small. The packets can be transmitted on any symbol boundary,rather than waiting for byte, word, or frame alignment as the fill datacan be interrupted without penalty.

Glossary of Terms

The language used in the claims and specification is to only have itsplain and ordinary meaning, except as explicitly defined below. Thewords in these definitions are to only have their plain and ordinarymeaning. Such plain and ordinary meaning is inclusive of all consistentdictionary definitions from the most recently published Webster'sdictionaries and Random House dictionaries. As used in the specificationand claims, the following definitions apply to these terms and commonvariations thereof identified below.

“Antenna” or “Antenna system” generally refers to an electrical device,or series of devices, in any suitable configuration, that convertselectric power into electromagnetic radiation. Such radiation may beeither vertically, horizontally, or circularly polarized at anyfrequency along the electromagnetic spectrum. Antennas transmitting withcircular polarity may have either right-handed or left-handedpolarization. In the case of radio waves, an antenna may transmit atfrequencies ranging along an electromagnetic spectrum from extremely lowfrequency (ELF) to extremely high frequency (EHF). An antenna or antennasystem designed to transmit radio waves may comprise an arrangement ofmetallic conductors (elements), electrically connected (often through atransmission line) to a receiver or transmitter. An oscillating currentof electrons forced through the antenna by a transmitter can create anoscillating magnetic field around the antenna elements, while the chargeof the electrons also creates an oscillating electric field along theelements. These time-varying fields radiate away from the antenna intospace as a moving transverse electromagnetic field wave. Conversely,during reception, the oscillating electric and magnetic fields of anincoming electromagnetic wave exert force on the electrons in theantenna elements, causing them to move back and forth, creatingoscillating currents in the antenna. These currents can then be detectedby receivers and processed to retrieve digital or analog signals ordata. Antennas can be designed to transmit and receive radio wavessubstantially equally in all horizontal directions (omnidirectionalantennas), or preferentially in a particular direction (directional orhigh gain antennas). In the latter case, an antenna may also includeadditional elements or surfaces which may or may not have any physicalelectrical connection to the transmitter or receiver. For example,parasitic elements, parabolic reflectors or horns, and other suchnon-energized elements serve to direct the radio waves into a beam orother desired radiation pattern. Thus antennas may be configured toexhibit increased or decreased directionality or “gain” by the placementof these various surfaces or elements. High gain antennas can beconfigured to direct a substantially large portion of the radiatedelectromagnetic energy in a given direction that may be vertical,horizontal, or any combination thereof. Antennas may also be configuredto radiate electromagnetic energy within a specific range of verticalangles (i.e. “takeoff angles) relative to the earth in order to focuselectromagnetic energy toward an upper layer of the atmosphere such asthe ionosphere. By directing electromagnetic energy toward the upperatmosphere at a specific angle, specific skip distances may be achievedat particular times of day by transmitting electromagnetic energy atparticular frequencies. Other examples of antennas include emitters andsensors that convert electrical energy into pulses of electromagneticenergy in the visible or invisible light portion of the electromagneticspectrum. Examples include light emitting diodes, lasers, and the likethat are configured to generate electromagnetic energy at frequenciesranging along the electromagnetic spectrum from far infrared to extremeultraviolet.

“Backend Communication Channel”, “Secondary Communication Channel”, or“Secondary Channel” generally refers to a communication pathway that isa main choice for transferring information. Typically, but not always,the secondary channel has one or more properties, such as latency orbandwidth, that make the channel less desirable over a primary channel.For example, a secondary channel can have a lower data rate and/orlatency as compared to a primary channel. A primary channel may supportthe transfer of information in one direction only, either directionalternately, or both directions simultaneously. The secondary channelcan for example include wired and wireless forms of communication.“Band” or “Frequency Bandwidth” generally refer to a contiguous range offrequencies defined by an upper and lower frequency. Frequency bandwidthis thus typically expressed as a number of hertz (cycles per second)representing the difference between the upper frequency and the lowerfrequency of the band and may or may not include the upper and lowerfrequencies themselves. A “band” can therefore be defined by a givenfrequency bandwidth for a given region and designated with generallyagreed on terms. For example, the “20 meter band” in the United Statesis assigned the frequency range from 14 MHz to 14.35 MHz thus defining afrequency bandwidth of 0.35 MHz or 350 KHz. In another example, theInternational Telecommunication Union (ITU) has designated the frequencyrange from 300 Mhz to 3 GHz as the “UHF band”.

“Checksum” generally refers to data derived from a block of digital datafor the purpose of detecting errors that may have been introduced duringits transmission and/or storage. Typically, the checksum data isrelatively small-sized. By themselves, checksums are often used toverify data integrity, but checksums are not typically relied upon toverify data authenticity. The procedure or process that generates thechecksum from a data input is called a checksum function or checksumalgorithm. Depending on the use case, a good checksum algorithm willusually output a significantly different value, even for small changesmade to the data input. When the computed checksum for a data inputmatches the stored value of a previously computed checksum, theprobability that the data has not been accidentally altered and/orcorrupted is high. Some checksum algorithm techniques include paritybyte, sum complement, and position-dependent algorithms. Check digitsand parity bits are special cases of checksums that are usuallyappropriate for small blocks of data. Some error-correcting codes arebased on special checksums which not only detect common errors, but theerror correcting code in some cases further helps in the recovery of theoriginal data.

“Command” or “Command Data” generally refers to one or more directives,instructions, algorithms, or rules controlling a machine to take one ormore actions, alone or in combination. A command may be stored,transferred, transmitted, or otherwise processed in any suitable manner.For example, a command may be stored in a memory or transmitted over acommunication network as electromagnetic radiation at any suitablefrequency passing through any suitable medium.

“Communication Link” generally refers to a connection between two ormore communicating entities and may or may not include a communicationschannel between the communicating entities. The communication betweenthe communicating entities may occur by any suitable means. For examplethe connection may be implemented as an actual physical link, anelectrical link, an electromagnetic link, a logical link, or any othersuitable linkage facilitating communication. In the case of an actualphysical link, communication may occur by multiple components in thecommunication link configured to respond to one another by physicalmovement of one element in relation to another. In the case of anelectrical link, the communication link may be composed of multipleelectrical conductors electrically connected to form the communicationlink. In the case of an electromagnetic link, elements of the connectionmay be implemented by sending or receiving electromagnetic energy at anysuitable frequency, thus allowing communications to pass aselectromagnetic waves. These electromagnetic waves may or may not passthrough a physical medium such as an optical fiber, or through freespace, or any combination thereof. Electromagnetic waves may be passedat any suitable frequency including any frequency in the electromagneticspectrum. In the case of a logical link, the communication links may bea conceptual linkage between the sender and recipient such as atransmission station in the receiving station. Logical link may includeany combination of physical, electrical, electromagnetic, or other typesof communication links.

“Communication Node” generally refers to a physical or logicalconnection point, redistribution point or endpoint along a communicationlink. A physical network node is generally referred to as an activeelectronic device attached or coupled to a communication link, eitherphysically, logically, or electromagnetically. A physical node iscapable of sending, receiving, or forwarding information over acommunication link. A communication node may or may not include acomputer, processor, transmitter, receiver, repeater, and/ortransmission lines, or any combination thereof.

“Computer” generally refers to any computing device configured tocompute a result from any number of input values or variables. Acomputer may include a processor for performing calculations to processinput or output. A computer may include a memory for storing values tobe processed by the processor, or for storing the results of previousprocessing. A computer may also be configured to accept input and outputfrom a wide array of input and output devices for receiving or sendingvalues. Such devices include other computers, keyboards, mice, visualdisplays, printers, industrial equipment, and systems or machinery ofall types and sizes. For example, a computer can control a network ornetwork interface to perform various network communications uponrequest. The network interface may be part of the computer, orcharacterized as separate and remote from the computer. A computer maybe a single, physical, computing device such as a desktop computer, alaptop computer, or may be composed of multiple devices of the same typesuch as a group of servers operating as one device in a networkedcluster, or a heterogeneous combination of different computing devicesoperating as one computer and linked together by a communicationnetwork. The communication network connected to the computer may also beconnected to a wider network such as the Internet. Thus a computer mayinclude one or more physical processors or other computing devices orcircuitry, and may also include any suitable type of memory. A computermay also be a virtual computing platform having an unknown orfluctuating number of physical processors and memories or memorydevices. A computer may thus be physically located in one geographicallocation or physically spread across several widely scattered locationswith multiple processors linked together by a communication network tooperate as a single computer. The concept of “computer” and “processor”within a computer or computing device also encompasses any suchprocessor or computing device serving to make calculations orcomparisons as part of the disclosed system. Processing operationsrelated to threshold comparisons, rules comparisons, calculations, andthe like occurring in a computer may occur, for example, on separateservers, the same server with separate processors, or on a virtualcomputing environment having an unknown number of physical processors asdescribed above. A computer may be optionally coupled to one or morevisual displays and/or may include an integrated visual display.Likewise, displays may be of the same type, or a heterogeneouscombination of different visual devices. A computer may also include oneor more operator input devices such as a keyboard, mouse, touch screen,laser or infrared pointing device, or gyroscopic pointing device to namejust a few representative examples. Also, besides a display, one or moreother output devices may be included such as a printer, plotter,industrial manufacturing machine, 3D printer, and the like. As such,various display, input and output device arrangements are possible.Multiple computers or computing devices may be configured to communicatewith one another or with other devices over wired or wirelesscommunication links to form a network. Network communications may passthrough various computers operating as network appliances such asswitches, routers, firewalls or other network devices or interfacesbefore passing over other larger computer networks such as the Internet.Communications can also be passed over the network as wireless datatransmissions carried over electromagnetic waves through transmissionlines or free space. Such communications include using Wi-Fi or otherWireless Local Area Network (WLAN) or a cellular transmitter/receiver totransfer data.

“Critical angle” generally refers to the highest angle with respect to avertical line extending to the center of the Earth at which anelectromagnetic wave at a specific frequency can be returned to theearth using skywave propagation.

“Critical Frequency” generally refers to the highest frequency that willbe returned to the Earth when transmitted vertically under givenionospheric conditions using sky-wave propagation.

“Cyclic Redundancy Check” or “CRC” generally refers to anerror-detecting code or technique to detect errors in digital data. Forexample, CRC is commonly used in digital networks and/or storage devicesto detect accidental changes to raw data. CRC is based on binarydivision, and CRC is also sometimes referred to as polynomial codechecksum. With CRC, blocks of data get encoded with or attached a shortcheck value that is based on the remainder of a polynomial division ofthe contents of the blocks of data. During retrieval or decoding, thecalculation is repeated. When the check values do not match, correctiveaction can be taken against data corruption. CRCs can be further used tofacilitate error correction. The check or data verification value is aredundancy because it expands the message without adding information.CRCs can be simple to implement in binary hardware, easy to analyzemathematically, and are good at detecting common errors caused by noisytransmission channels. Given the check value has a fixed length, thefunction that generates the check value is sometimes used as a hashfunction.

“Data” generally refers to one or more values of qualitative orquantitative variables that are usually the result of measurements. Datamay be considered “atomic” as being finite individual units of specificinformation. Data can also be thought of as a value or set of valuesthat includes a frame of reference indicating some meaning associatedwith the values. For example, the number “2” alone is a symbol thatabsent some context is meaningless. The number “2” may be considered“data” when it is understood to indicate, for example, the number ofitems produced in an hour. Data may be organized and represented in astructured format. Examples include a tabular representation using rowsand columns, a tree representation with a set of nodes considered tohave a parent-children relationship, or a graph representation as a setof connected nodes to name a few. The term “data” can refer tounprocessed data or “raw data” such as a collection of numbers,characters, or other symbols representing individual facts or opinions.Data may be collected by sensors in controlled or uncontrolledenvironments, or generated by observation, recording, or by processingof other data. The word “data” may be used in a plural or singular form.The older plural form “datum” may be used as well.

“Data Bandwidth” generally refers to the maximum throughput of a logicalor physical communication path in a communication system. Data bandwidthis a transfer rate that can be expressed in units of data transferredper second. In a digital communications network, the units of datatransferred are bits and the maximum throughput of a digitalcommunications network is therefore generally expressed in “bits persecond” or “bit/s.” By extension, the terms “kilobit/s” or “Kbit/s”,“Megabit/s” or “Mbit/s”, and “Gigabit/s” or “Gbit/s” can also be used toexpress the data bandwidth of a given digital communications network.Data networks may be rated according to their data bandwidth performancecharacteristics according to specific metrics such as “peak bit rate”,“mean bit rate”, “maximum sustained bit rate”, “information rate”, or“physical layer useful bit rate.” For example, bandwidth tests measurethe maximum throughput of a computer network. The reason for this usageis that according to Hartley's Law, the maximum data rate of a physicalcommunication link is proportional to its frequency bandwidth in hertz.Data bandwidth may also be characterized according to the maximumtransfer rate for a particular communications network. For example:

“Low Data Bandwidth” generally refers to a communications network with amaximum data transfer rate that is less than or about equal to 1,000,000units of data per second. For example, in a digital communicationsnetwork, the unit of data is a bit. Therefore low data bandwidth digitalcommunications networks are networks with a maximum transfer rate thatis less than or about equal to 1,000,000 bits per second (1 Mbits/s).

“High Data Bandwidth” generally refers to a communications network witha maximum data transfer rate that is greater than about 1,000,000 unitsof data per second. For example, a digital communications network with ahigh data bandwidth is a digital communications network with a maximumtransfer rate that is greater than about 1,000,000 bits per second (1Mbits/s).

“Demodulation” generally refers to a process of extracting an originalinformation-bearing signal from a carrier wave.

“Demodulator” or “Detector” generally refers to a device, such as anelectronic circuit and/or computer, that extracts original informationfrom a received modulated waveform based on one or more properties ofthe waveform. For example, these properties of the waveform can includeamplitude, frequency, phase, and harmonics as well as other properties.After reception of the modulated carrier, the demodulator recovers theoriginal modulating signal by the process of demodulation or detection.One or more modulators can be integrated with one or more demodulatorsto form a modulator-demodulator (modem). As such, the term demodulatormay further refer to one or more parts, components, and/or software thatdemodulate within a modem.

“Electromagnet Radiation” generally refers to energy radiated byelectromagnetic waves. Electromagnetic radiation is produced from othertypes of energy, and is converted to other types when it is destroyed.Electromagnetic radiation carries this energy as it travels moving awayfrom its source at the speed of light (in a vacuum). Electromagneticradiation also carries both momentum and angular momentum. Theseproperties may all be imparted to matter with which the electromagneticradiation interacts as it moves outwardly away from its source.Electromagnetic radiation changes speed as it passes from one medium toanother. When transitioning from one media to the next, the physicalproperties of the new medium can cause some or all of the radiatedenergy to be reflected while the remaining energy passes into the newmedium. This occurs at every junction between media that electromagneticradiation encounters as it travels. The photon is the quantum of theelectromagnetic interaction and is the basic constituent of all forms ofelectromagnetic radiation. The quantum nature of light becomes moreapparent at high frequencies as electromagnetic radiation behaves morelike particles and less like waves as its frequency increases.

“Electromagnetic Spectrum” generally refers to the range of all possiblefrequencies of electromagnetic radiation.

“Electromagnetic Waves” generally refers to waves having a separateelectrical and a magnetic component. The electrical and magneticcomponents of an electromagnetic wave oscillate in phase and are alwaysseparated by a 90 degree angle. Electromagnetic waves can radiate from asource to create electromagnetic radiation capable of passing through amedium or through a vacuum. Electromagnetic waves include wavesoscillating at any frequency in the electromagnetic spectrum including,but not limited to, radio waves, visible and invisible light, X-rays,and gamma-rays.

“Error Correction Code”, “Error Correcting Code”, or “ECC” generallyrefers to data and/or algorithms for expressing a sequence of numbers orother data such that any errors which are introduced can be detected andcorrected within certain limitations based on the remaining numbers ordata. ECC is typically used for controlling errors in data overunreliable and/or noisy communication channels. For instance, the senderencodes the message with a redundant in the form of an ECC. There aretwo main categories of ECCs, block codes and convolution codes. Somenon-limiting examples of ECC codes include AN, BCH, Berger,constant-weight, convolutional, cyclic redundancy check (CRC), expander,group, Golay, Goppa, Hadamard, Hagelbarger, Hamming code, Latin squarebased, lexicographic, long, low-density parity-check (i.e., Gallagercode), LT, polar, raptor, Reed-Solomon error correction, Reed-Muller,repeat-accumulate, repetition (e.g., triple modular redundancy), spinal,rateless, nonlinear, tornado, near-optimal erasure correcting, turbocode, and Walsh-Hadamard codes.

“Fiber-optic Communication” generally refers to a method of transmittingdata from one place to another by sending pulses of electromagneticenergy through an optical fiber. The transmitted energy may form anelectromagnetic carrier wave that can be modulated to carry data.Fiber-optic communication lines that use optical fiber cables totransmit data can be configured to have a high data bandwidth. Forexample, fiber-optic communication lines may have a high data bandwidthof up to about 15 Tbit/s, about 25 Tbit/s, about 100 Tbit/s, about 1Pbit/s or more. Opto-electronic repeaters may be used along afiber-optic communication line to convert the electromagnetic energyfrom one segment of fiber-optic cable into an electrical signal. Therepeater can retransmit the electrical signal as electromagnetic energyalong another segment of fiber-optic cable at a higher signal strengththan it was received.

“Financial Instrument” generally refers to a tradable asset of any kind.General examples include, but are not limited to, cash, evidence of anownership interest in an entity, or a contractual right to receive ordeliver cash or another financial instrument. Specific examples includebonds, bills (e.g. commercial paper and treasury bills), stock, loans,deposits, certificates of deposit, bond futures or options on bondfutures, short-term interest rate futures, stock options, equityfutures, currency futures, interest rate swaps, interest rate caps andfloors, interest rate options, forward rate agreements, stock options,foreign-exchange options, foreign-exchange swaps, currency swaps, or anysort of derivative.

“Forward Error Correction” or FEC generally refers to a technique usedfor controlling errors in data transmission over unreliable or noisycommunication channels. Typically, but not always, a sender encodes themessage in a redundant way by using an error-correction code (ECC). Thisredundancy allows a receiver to detect a limited number of errors thatmay occur anywhere in the message, and the redundancy often allows theseerrors to be corrected without retransmission. FEC gives the receiverthe ability to correct errors without needing a reverse channel torequest retransmission of data. However, higher forward channelbandwidth is typically required. FEC can be used in situations whereretransmissions are costly or impossible, such as one-way communicationlinks and when transmitting to multiple receivers in multicast. FEC iscommonly used in modems. FEC information can also be added to massstorage devices to enable recovery of corrupted data. There aregenerally two types of FEC code categories, block codes and convolutioncodes. FEC block codes work on fixed-size blocks (or packets) of bits orsymbols of predetermined size. Some non-limiting examples of block codesinclude Reed-Solomon, Golay, BCH, multidimensional parity, and Hammingcodes. Typical block codes are usually decoded using hard-decisionalgorithms in which for every input and output signal a hard decision ismade whether it corresponds to a one or a zero bit. Convolutional FECcodes work on bit or symbol streams of arbitrary length. Convolutionalcodes are typically decoded using soft-decision algorithms like theViterbi, MAP or BCJR algorithms that process (discretized) analogsignals, and which allow for much higher error-correction performancethan hard-decision decoding. Convolutional FEC codes are most often softdecoded with the Viterbi algorithm, though other algorithms can be used.Viterbi decoding allows asymptotically optimal decoding efficiency withincreasing constraint length of the convolutional code, but at theexpense of exponentially increasing complexity. A convolutional codethat is terminated is also a block code in that it encodes a block ofinput data, but the block size of a convolutional code is generallyarbitrary, while block codes have a fixed size dictated by theiralgebraic characteristics. Types of termination for convolutional codesinclude tail-biting and bit-flushing. Some other non-limiting examplesof FEC techniques include turbo coding, low density parity check (LDPC),interleaving, and local decoding. Many FEC coders (but not all) can alsogenerate a bit-error rate (BER) signal which can be used as feedback tofine-tune the analog receiving electronics.

“Ground” is used more in an electrical/electromagnetic sense andgenerally refers to the Earth's surface including land and bodies ofwater, such as oceans, lakes, and rivers.

“Ground-wave Propagation” generally refers to a transmission method inwhich one or more electromagnetic waves are conducted via the boundaryof the ground and atmosphere to travel along the ground. Theelectromagnetic wave propagates by interacting with the semi-conductivesurface of the earth. In essence, the wave clings to the surfaces so asto follow the curvature of the earth. Typically, but not always, theelectromagnetic wave is in the form of a ground or surface wave formedby low-frequency radio waves.

“Identifier” generally refers to a name that identifies (that is, labelsthe identity of) either a unique thing or a unique class of things,where the “object” or class may be an idea, physical object (or classthereof), or physical substance (or class thereof). The abbreviation“ID” often refers to identity, identification (the process ofidentifying), or an identifier (that is, an instance of identification).An identifier may or may not include words, numbers, letters, symbols,shapes, colors, sounds, or any combination of those. The words, numbers,letters, or symbols may follow an encoding system (wherein letters,digits, words, or symbols represent ideas or longer identifiers) or theymay simply be arbitrary. When an identifier follows an encoding system,it is often referred to as a code or ID code. Identifiers that do notfollow any encoding scheme are often said to be arbitrary IDs becausethey are arbitrarily assigned without meaning in any other contextbeyond identifying something.

“Ionosphere” generally refers to the layer of the Earth's atmospherethat contains a high concentration of ions and free electrons and isable to reflect radio waves. The ionosphere includes the thermosphere aswell as parts of the mesosphere and exosphere. The ionosphere extendsfrom about 25 to about 600 miles (about 40 to 1,000 km) above theearth's surface. The ionosphere includes a number of layers that undergoconsiderable variations in altitude, density, and thickness, dependingupon a number of factors including solar activity, such as sunspots.

“Jitter” generally refers to a variable delay in the receipt of atransmitted message. For example, jitter arises as messages arrive at aninput at varying intervals, and as a result, the receiver of the messagehas to wait a variable time before a data slot is available for messagetransport.

“Latency” generally refers to the time interval between a cause and aneffect in a system. Latency is physically a consequence of the limitedvelocity with which any physical interaction can propagate throughout asystem. Latency is physically a consequence of the limited velocity withwhich any physical interaction can propagate. The speed at which aneffect can propagate through a system is always lower than or equal tothe speed of light. Therefore every physical system that includes somedistance between the cause and the effect will experience some kind oflatency. For example, in a communication link or communications network,latency generally refers to the minimum time it takes for data to passfrom one point to another. Latency with respect to communicationsnetworks may also be characterized as the time it takes energy to movefrom one point along the network to another. With respect to delayscaused by the propagation of electromagnetic energy following aparticular propagation path, latency can be categorized as follows:

“Low Latency” generally refers to a period of time that is less than orabout equal to a propagation time that is 10% greater than the timerequired for light to travel a given propagation path in a vacuum.Expressed as a formula, low latency is defined as follows:

${latency_{low}} \leq {\frac{d}{c} \cdot k}$

where:

-   -   d=distance (miles)    -   c=the speed of light in a vacuum (186,000 miles/sec)    -   k=a scalar constant of 1.1

For example, light can travel 25,000 miles through a vacuum in about0.1344 seconds. A “low latency” communication link carrying data overthis 25,000 mile propagation path would therefore be capable of passingat least some portion of the data over the link in about 0.14784 secondsor less.

“High Latency” generally refers to a period of time that is over 10%greater than the time required for light to travel a given propagationpath in a vacuum. Expressed as a formula, high latency is defined asfollows:

${latency_{high}} > {\frac{d}{c} \cdot k}$

where:

-   -   d=distance (miles)    -   c=the speed of light in a vacuum (186,000 miles/sec)    -   k=a scalar constant of 1.1

For example, light can travel 8,000 miles through a vacuum in about0.04301 seconds. A “high latency” communication link carrying data overthis transmission path would therefore be capable of passing at leastsome portion of the data over the link in about 0.04731 seconds or more.

The “high” and “low” latency of a network may be independent of the databandwidth. Some “high” latency networks may have a high transfer ratethat is higher than a “low” latency network, but this may not always bethe case. Some “low” latency networks may have a data bandwidth thatexceeds the bandwidth of a “high” latency network.

“Maximum Usable Frequency (MUF)” generally refers to the highestfrequency that is returned to the earth using skywave propagation.

“Memory” generally refers to any storage system or device configured toretain data or information. Each memory may include one or more types ofsolid-state electronic memory, magnetic memory, or optical memory, justto name a few. By way of non-limiting example, each memory may includesolid-state electronic Random Access Memory (RAM), SequentiallyAccessible Memory (SAM) (such as the First-In, First-Out (FIFO) varietyor the Last-In-First-Out (LIFO) variety), Programmable Read Only Memory(PROM), Electronically Programmable Read Only Memory (EPROM), orElectrically Erasable Programmable Read Only Memory (EEPROM); an opticaldisc memory (such as a DVD or CD ROM); a magnetically encoded hard disc,floppy disc, tape, or cartridge media; or a combination of any of thesememory types. Also, each memory may be volatile, nonvolatile, or ahybrid combination of volatile and nonvolatile varieties.

“Message” generally refers to a discrete unit of communication intendedby a source for consumption by a recipient or group of recipients.

“Modem” or “Modulator-Demodulator” generally refers to a device, such asan electronic circuit and/or computer, that performs the functions ofmodulation and demodulation of a signal such as through a modulator anda demodulator.

“Modulation” generally refers to the process of varying one or moreproperties of a periodic waveform, called the carrier signal, with amodulating signal that typically contains information to be transmitted.

“Modulator” generally refers to a device, such as an electronic circuitand/or computer, that varies one or more properties of a periodicwaveform, called the carrier signal, with a modulating signal thattypically contains information to be transmitted. For example, theseproperties of the waveform can include amplitude, frequency, phase, andharmonics as well as other properties. By way of a non-limiting example,the modulator can control the parameters of a high-frequencyelectromagnetic information carrier in accordance with electricalsignals of the transmitted message. One or more modulators can beintegrated with one or more demodulators to form a modulator-demodulator(modem). As such, the term modulator may further refer to one or moreparts, components, and/or software that functions as a modulator withina modem.

“Network” or “Computer Network” generally refers to a telecommunicationsnetwork that allows computers to exchange data. Computers can pass datato each other along data connections by transforming data into acollection of datagrams or packets. The connections between computersand the network may be established using either cables, optical fibers,or via electromagnetic transmissions such as for wireless networkdevices. Computers coupled to a network may be referred to as “nodes” oras “hosts” and may originate, broadcast, route, or accept data from thenetwork. Nodes can include any computing device such as personalcomputers, phones, and servers as well as specialized computers thatoperate to maintain the flow of data across the network, referred to as“network devices”. Two nodes can be considered “networked together” whenone device is able to exchange information with another device, whetheror not they have a direct connection to each other. A network may haveany suitable network topology defining the number and use of the networkconnections. The network topology may be of any suitable form and mayinclude point-to-point, bus, star, ring, mesh, or tree. A network may bean overlay network which is virtual and is configured as one or morelayers that use or “lay on top of” other networks.

“Non-skywave propagation” generally refers to all forms of transmission,wired and/or wireless, in which the information is not transmitted byreflecting an electromagnetic wave from the ionosphere.

“Optical Fiber” generally refers to an electromagnetic waveguide havingan elongate conduit that includes a substantially transparent mediumthrough which electromagnetic energy travels as it traverses the longaxis of the conduit. Electromagnetic radiation may be maintained withinthe conduit by total internal reflection of the electromagneticradiation as it traverses the conduit. Total internal reflection isgenerally achieved using optical fibers that include a substantiallytransparent core surrounded by a second substantially transparentcladding material with a lower index of refraction than the core.Optical fibers are generally constructed of dielectric material that isnot electrically conductive but is substantially transparent. Suchmaterials may or may not include any combination of extruded glass suchas silica, fluoride glass, phosphate glass, Chalcogenide glass, orpolymeric material such as various types of plastic, or other suitablematerial and may be configured with any suitable cross-sectional shape,length, or dimension. Examples of electromagnetic energy that may besuccessfully passed through optical fibers include electromagnetic wavesin the near-infrared, mid-infrared, and visible light portion of theelectromagnetic spectrum, although electromagnetic energy of anysuitable frequency may be used.

“Optimum Working Frequency” generally refers to the frequency thatprovides the most consistent communication path via sky-wavepropagation. It can vary over time depending on number of factors, suchas ionospheric conditions and time of day. For transmissions using theF2 layer of the ionosphere the working frequency is generally around 85%of the MUF, and for the E layer, the optimum working frequency willgenerally be near the MUF.

“Polarization” generally refers to the orientation of the electric field(“E-plane”) of a radiated electromagnetic energy wave with respect tothe Earth's surface and is determined by the physical structure andorientation of the radiating antenna. Polarization can be consideredseparately from an antenna's directionality. Thus, a simple straightwire antenna may have one polarization when mounted substantiallyvertically, and a different polarization when mounted substantiallyhorizontally. As a transverse wave, the magnetic field of a radio waveis at right angles to that of the electric field, but by convention,talk of an antenna's “polarization” is understood to refer to thedirection of the electric field. Reflections generally affectpolarization. For radio waves, one important reflector is the ionospherewhich can change the wave's polarization. Thus for signals received viareflection by the ionosphere (a skywave), a consistent polarizationcannot be expected. For line-of-sight communications or ground wavepropagation, horizontally or vertically polarized transmissionsgenerally remain in about the same polarization state at the receivinglocation. Matching the receiving antenna's polarization to that of thetransmitter may be especially important in ground wave or line-of-sightpropagation but may be less important in skywave propagation. Anantenna's linear polarization is generally along the direction (asviewed from the receiving location) of the antenna's currents when sucha direction can be defined. For instance, a vertical whip antenna orWi-Fi antenna vertically oriented will transmit and receive in thevertical polarization. Antennas with horizontal elements, such as mostrooftop TV antennas, are generally horizontally polarized (becausebroadcast TV usually uses horizontal polarization). Even when theantenna system has a vertical orientation, such as an array ofhorizontal dipole antennas, the polarization is in the horizontaldirection corresponding to the current flow. Polarization is the sum ofthe E-plane orientations over time projected onto an imaginary planeperpendicular to the direction of motion of the radio wave. In the mostgeneral case, polarization is elliptical, meaning that the polarizationof the radio waves varies over time. Two special cases are linearpolarization (the ellipse collapses into a line) as discussed above, andcircular polarization (in which the two axes of the ellipse are equal).In linear polarization the electric field of the radio wave oscillatesback and forth along one direction; this can be affected by the mountingof the antenna but usually the desired direction is either horizontal orvertical polarization. In circular polarization, the electric field (andmagnetic field) of the radio wave rotates at the radio frequencycircularly around the axis of propagation.

“Primary Communication Channel” or “Primary Channel” generally refers toa communication pathway that is a first choice for transferringinformation. Typically, but not always, the primary communicationchannel has one or more properties, such as latency or bandwidth, thatis desirable over others. For example, a primary communication channelcan have the highest data rate of all the channels sharing a commoninterface. A primary communication channel may support the transfer ofinformation in one direction only, either direction alternately, or bothdirections simultaneously. The primary communication channel can forexample include wired and wireless forms of communication.

“Processor” generally refers to one or more electronic componentsconfigured to operate as a single unit configured or programmed toprocess input to generate an output. Alternatively, when of amulti-component form, a processor may have one or more componentslocated remotely relative to the others. One or more components of eachprocessor may be of the electronic variety defining digital circuitry,analog circuitry, or both. In one example, each processor is of aconventional, integrated circuit microprocessor arrangement. A processoralso includes an Application-Specific Integrated Circuit (ASIC). An ASICis an Integrated Circuit (IC) customized to perform a specific series oflogical operations in controlling a computer to perform specific tasksor functions. An ASIC is an example of a processor for a special purposecomputer, rather than a processor configured for general-purpose use. Anapplication-specific integrated circuit generally is not reprogrammableto perform other functions and may be programmed once when it ismanufactured. In another example, a processor may be of the “fieldprogrammable” type. Such processors may be programmed multiple times “inthe field” to perform various specialized or general functions afterthey are manufactured. A field-programmable processor may include aField-Programmable Gate Array (FPGA) in an integrated circuit in theprocessor. FPGA may be programmed to perform a specific series ofinstructions which may be retained in nonvolatile memory cells in theFPGA. The FPGA may be configured by a customer or a designer using ahardware description language (HDL). An FPGA may be reprogrammed usinganother computer to reconfigure the FPGA to implement a new set ofcommands or operating instructions. Such an operation may be executed inany suitable means such as by a firmware upgrade to the processorcircuitry. Just as the concept of a computer is not limited to a singlephysical device in a single location, so also the concept of a“processor” is not limited to a single physical logic circuit or packageof circuits but includes one or more such circuits or circuit packagespossibly contained within or across multiple computers in numerousphysical locations. In a virtual computing environment, an unknownnumber of physical processors may be actively processing data, and theunknown number may automatically change over time as well. The conceptof a “processor” includes a device configured or programmed to makethreshold comparisons, rules comparisons, calculations, or performlogical operations applying a rule to data yielding a logical result(e.g. “true” or “false”). Processing activities may occur in multiplesingle processors on separate servers, on multiple processors in asingle server with separate processors, or on multiple processorsphysically remote from one another in separate computing devices.

“Pseudorandom Binary Sequence” or “PRBS” generally refers to a binarysequence generated with a deterministic algorithm that is difficult topredict and exhibits statistical behavior similar to a truly randomsequence.

“Radio” generally refers to electromagnetic radiation in the frequenciesthat occupy the range from 3 kHz to 300 GHz.

“Radio horizon” generally refers to the locus of points at which directrays from an antenna are tangential to the ground. The radio horizon canbe approximated by the following equation:d≅√{square root over (2h_(t))}+√{square root over (2h_(r))}

where:

d=radio horizon (miles)

h_(t)=transmitting antenna height (feet)

h_(r)=receiving antenna height (feet).

“Receive” generally refers to accepting something transferred,communicated, conveyed, relayed, dispatched, or forwarded. The conceptmay or may not include the act of listening or waiting for something toarrive from a transmitting entity. For example, a transmission may bereceived without knowledge as to who or what transmitted it. Likewisethe transmission may be sent with or without knowledge of who or what isreceiving it. To “receive” may include, but is not limited to, the actof capturing or obtaining electromagnetic energy at any suitablefrequency in the electromagnetic spectrum. Receiving may occur bysensing electromagnetic radiation. Sensing electromagnetic radiation mayinvolve detecting energy waves moving through or from a medium such as awire or optical fiber. Receiving includes receiving digital signalswhich may define various types of analog or binary data such as signals,datagrams, packets and the like.

“Receiving Station” generally refers to a receiving device, or to alocation facility having multiple devices configured to receiveelectromagnetic energy. A receiving station may be configured to receivefrom a particular transmitting entity, or from any transmitting entityregardless of whether the transmitting entity is identifiable in advanceof receiving the transmission.

“Remote” generally refers to any physical, logical, or other separationbetween two things. The separation may be relatively large, such asthousands or millions of miles or kilometers, or small such asnanometers or millionths of an inch. Two things “remote” from oneanother may also be logically or physically coupled or connectedtogether.

“Satellite Communication” or “Satellite Propagation” generally refers totransmitting one or more electromagnetic signals to a satellite which inturn reflects and/or retransmits the signal to another satellite orstation.

“Size” generally refers to the extent of something; a thing's overalldimensions or magnitude; how big something is. For physical objects,size may be used to describe relative terms such as large or larger,high or higher, low or lower, small or smaller, and the like. Size ofphysical objects may also be given in fixed units such as a specificwidth, length, height, distance, volume, and the like expressed in anysuitable units. For data transfer, size may be used to indicate arelative or fixed quantity of data being manipulated, addressed,transmitted, received, or processed as a logical or physical unit. Sizemay be used in conjunction with the amount of data in a data collection,data set, data file, or other such logical unit. For example, a datacollection or data file may be characterized as having a “size” of 35Mbytes, or a communication link may be characterized as having a databandwidth with a “size” of 1000 bits per second.

“Skip distance” generally refers to the minimum distance from atransmitter to where a wave from skywave propagation can be returned tothe Earth. To put it another way, the skip distance is the minimumdistance that occurs at the critical angle for sky-wave propagation.

“Skip Zone” or “Quiet Zone” generally refers to an area between thelocation where a ground wave from ground wave propagation is completelydissipated and the location where the first skywave returns usingskywave propagation. In the skip zone, no signal for a giventransmission can be received.

“Skywave Propagation” refers generally to a transmission method in whichone or more electromagnetic-waves radiated from an antenna are refractedfrom the ionosphere back to the ground. Skywave propagation furtherincludes tropospheric scatter transmissions. In one form, a skippingmethod can be used in which the waves refracted from the ionosphere arereflected by the ground back up to the ionosphere. This skipping canoccur more than once.

“Space-wave Propagation” or sometimes referred to as “Direct WavePropagation” or “Line-of-sight Propagation” generally refers to atransmission method in which one or more electromagnetic waves aretransmitted between antennas that are generally visible to one another.The transmission can occur via direct and/or ground reflected spacewaves. Generally speaking, the antenna height and curvature of the earthare limiting factors for the transmission distances for space-wavepropagation. The actual radio horizon for a direct line of sight islarger than the visible or geometric line of sight due to diffractioneffects; that is, the radio horizon is about ⅘ greater than thegeometric line of sight.

“Spread Spectrum” generally refers to a transmission method thatincludes sending a portion of a transmitted signal over multiplefrequencies. The transmission over multiple frequencies may occursimultaneously by sending a portion of the signal on variousfrequencies. In this example, a receiver must listen to all frequenciessimultaneously in order to reassemble the transmitted signal. Thetransmission may also be spread over multiple frequencies by “hopping”signals. A signal hopping scenario includes transmitting the signal forsome period of time over a first frequency, switching to transmit thesignal over a second frequency for a second period of time, beforeswitching to a third frequency for a third period of time, and so forth.The receiver and transmitter must be synchronized in order to switchfrequencies together. This process of “hopping” frequencies may beimplemented in a frequency-hopping pattern that may change over time(e.g. every hour, every 24 hours, and the like).

“Stratosphere” generally refers to a layer of the earth's atmosphereextending from the troposphere to about 25 to 35 miles above the earthsurface.

“Symbol” generally refers to a waveform, a state or a significantcondition of the communication channel that persists, for a fixed periodof time. For digital baseband transmissions, a symbol may be in the formof a pulse, and a symbol may be in the form of a tone in passbandtransmissions using modems. A transmitter or other device places symbolson one or more channels, and the receiver detects the sequence ofsymbols in order to reconstruct the transmitted data. In some cases,there may be a direct correspondence between a symbol and a small unitof data. For instance, each symbol can encode one or several bits. Thedata may also be represented by the transitions between symbols, and/orby a sequence of several symbols.

“Transceiver” generally refers to a device that includes both atransmitter and a receiver that share common circuitry and/or a singlehousing. Transceivers are typically, but not always, designed totransmit and receive electronic signals, such as analog and/or digitalradio signals.

“Transfer Rate” generally refers to the rate at which something is movedfrom one physical or logical location to another. In the case of acommunication link or communication network, a transfer rate may becharacterized as the rate of data transfer over the link or network.Such a transfer rate may be expressed in “bits per second” and may belimited by the maximum data bandwidth for a given network orcommunication link used to carry out a transfer of data.

“Transmission Line” generally refers to a specialized physical structureor series of structures designed to carry electromagnetic energy fromone location to another, usually without radiating the electromagneticenergy through free space. A transmission line operates to retain andtransfer electromagnetic energy from one location to another whileminimizing latency and power losses incurred as the electromagneticenergy passes through the structures in the transmission line. Examplesof transmission lines that may be used in communicating radio wavesinclude twin lead, coaxial cable, microstrip, strip line, twisted-pair,star quad, lecher lines, various types of waveguide, or a simple singlewire line. Other types of transmission lines such as optical fibers maybe used for carrying higher frequency electromagnetic radiation such asvisible or invisible light.

“Transmission Path” or “Propagation Path” generally refers to a pathtaken by electromagnetic energy passing through space or through amedium. This can include transmissions through a transmission line. Inthis case, the transmission path is defined by, follows, is containedwithin, passes through, or generally includes the transmission line. Atransmission or propagation path need not be defined by a transmissionline. A propagation or transmission path can be defined byelectromagnetic energy moving through free space or through theatmosphere such as in skywave, ground wave, line-of-sight, or otherforms of propagation. In that case, the transmission path can becharacterized as any path along which the electromagnetic energy passesas it is moves from the transmitter to the receiver, including any skip,bounce, scatter, or other variations in the direction of the transmittedenergy.

“Transmission Station” generally refers to a transmitting device, or toa location or facility having multiple devices configured to transmitelectromagnetic energy. A transmission station may be configured totransmit to a particular receiving entity, to any entity configured toreceive transmission, or any combination thereof.

“Transmission Time” generally refers to is the amount of time from thebeginning until the end of a message transmission in a communicationnetwork. In the case of a digital message, the transmission time is thetime from the first bit until the last bit of a message has left thetransmitting node. For a digital packet, the packet transmission timecan be obtained from the packet size and bit rate. The transmission timeshould not be confused with propagation delay which refers to the timeit takes for the first bit to travel from a sender to a receiver.“Transmit” generally refers to causing something to be transferred,communicated, conveyed, relayed, dispatched, or forwarded. The conceptmay or may not include the act of conveying something from atransmitting entity to a receiving entity. For example, a transmissionmay be received without knowledge as to who or what transmitted it.Likewise the transmission may be sent with or without knowledge of whoor what is receiving it. To “transmit” may include, but is not limitedto, the act of sending or broadcasting electromagnetic energy at anysuitable frequency in the electromagnetic spectrum. Transmissions mayinclude digital signals which may define various types of binary datasuch as datagrams, packets and the like. A transmission may also includeanalog signals.

“Triggering Data” generally refers to data that includes triggeringinformation identifying one or more commands to execute. The triggeringdata and the command data may occur together in a single transmission ormay be transmitted separately along a single or multiple communicationlinks.

“Troposphere” generally refers to the lowest portion of the earth'satmosphere. The troposphere extends about 11 miles above the surface ofthe earth in the mid-latitudes, up to 12 miles in the tropics, and about4.3 miles in winter at the poles.

“Tropospheric Scatter Transmission” generally refers to a form ofskywave propagation in which one or more electromagnetic waves, such asradio waves, are aimed at the troposphere. While not certain as to itscause, a small amount of energy of the waves is scattered forwards to areceiving antenna. Due to severe fading problems, diversity receptiontechniques (e.g., space, frequency, and/or angle diversity) aretypically used.

“Wave Guide” generally refers to a transmission line configured toguides waves such as electromagnetic waves occurring at any frequencyalong the electromagnetic spectrum. Examples include any arrangement ofconductive or insulative material configured to transfer lower frequencyelectromagnetic radiation ranging along the electromagnetic spectrumfrom extremely low frequency to extremely high frequency waves. Othersspecific examples include optical fibers guiding high-frequency light orhollow conductive metal pipe used to carry high-frequency radio waves,particularly microwaves.

It should be noted that the singular forms “a,” “an,” “the,” and thelike as used in the description and/or the claims include the pluralforms unless expressly discussed otherwise. For example, if thespecification and/or claims refer to “a device” or “the device”, itincludes one or more of such devices.

It should be noted that directional terms, such as “up,” “down,” “top,”“bottom,” “lateral,” “longitudinal,” “radial,” “circumferential,”“horizontal,” “vertical,” etc., are used herein solely for theconvenience of the reader in order to aid in the reader's understandingof the illustrated embodiments, and it is not the intent that the use ofthese directional terms in any manner limit the described, illustrated,and/or claimed features to a specific direction and/or orientation.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges, equivalents, and modifications that come within the spirit ofthe inventions defined by the following claims are desired to beprotected. All publications, patents, and patent applications cited inthis specification are herein incorporated by reference as if eachindividual publication, patent, or patent application were specificallyand individually indicated to be incorporated by reference and set forthin its entirety herein.

REFERENCE NUMBERS

100 communication system 105 information source 110 informationdestination 115 communication channels 120 primary communication channel125 backend communication channel 130 distance 135 primary channellatency 140 primary channel bandwidth 145 backend channel latency 150backend channel bandwidth 200 communication system 204 low latency, lowbandwidth communication link 206 HF radio channel 208 high latency, highbandwidth communication link 212 first communication node 214transmission station 216 second communication node 218 receiving station220 atmosphere 224 electromagnetic waves 228 transmitting antenna 232receiving antenna 236 transmission line 240 transmission line 244transmission line 252 repeaters 256 earth 260 client 264 connection 266wireless connection 268 instruction processor 272 connection 405modulator 410 radio transmitter 415 fiber optic transmitter 420 fiberoptic cable 425 demodulator 430 radio receiver 435 fiber optic receiver500 communication system 505 high speed transmitter data network 510high speed receiver data network 600 transmitter system 605 highfrequency trading network 610 user data 615 transmission acknowledgementdata 620 transmitted data 700 diagram 705 time 710 user data packets 715user messages 720 fill data 725 high speed network packet transmissiontime 730 radio frequency channel message transmission time 735inter-message transmission time 800 flowchart 805 stage 810 stage 815stage 820 stage 825 stage 830 stage 900 diagram 905 stage 910 stage 915stage 920 stage 925 stage 930 stage 935 stage 1000 fill data generationsystem 1005 PRBS source 1010 receive FEC decoder 1015 receive CRCdetector 1100 diagram 1105 stage 1110 stage 1115 stage 1120 stage 1125stage 1130 stage

What is claimed is:
 1. A method, comprising: receiving a message from aprimary communication channel at a receiving station; wherein saidreceiving the message includes receiving the message through a messagedata stream; wherein the message data stream includes user data and filldata; wherein the user data has been encoded in accordance with a paritycheck code and an error correction scheme; wherein the fill data hasbeen encoded in accordance with the parity check code and the errorcorrection scheme; wherein the till data has been modified to fail aparity check code test; maintaining a signal lock on the message datastream through the fill data; detecting a message boundary of themessage through the parity check code in combination with the errorcorrection scheme; wherein said detecting the message boundary includesdetermining with the receiving station that the fill data has failed theparity check code test; and wherein said detecting the message boundaryincludes decoding with the receiving station the user data successfullythrough the parity check code and the error correction scheme.
 2. Themethod of claim 1, wherein the primary communication channel includes alow bandwidth, low latency communication link.
 3. The method of claim 2,wherein the primary communication channel includes a high frequencyradio channel.
 4. The method of claim 1, wherein the user data isencoded in an asynchronous manner in the message data stream.
 5. Themethod of claim 1, wherein the fill data includes a pseudorandom binarysequence (PRBS).
 6. The method of claim 5, wherein the fill dataincludes a version of the PRBS modified by the parity check code and theerror correction scheme.
 7. The method of claim 6, further comprising:detecting a false message with the version of the PRBS.
 8. The method ofclaim 7, wherein the version of the PRBS has been modified to fail aparity check code test.
 9. The method of claim 7, wherein the version ofthe PRBS has been modified to fail an error correction scheme test. 10.The method of claim 1, wherein the parity check code includes achecksum.
 11. The method of claim 1, wherein the parity check codeincludes a cyclic redundancy check (CRC).
 12. The method of claim 1,wherein the error correction scheme includes forward error correction(FEC).
 13. The method of claim 1, wherein the error correction schemeincludes a convolution code scheme.
 14. The method of claim 13, whereinthe error correction scheme includes a tail-biting Viterbi decodingalgorithm.
 15. The method of claim 1, wherein the error correctionscheme includes a block code scheme.
 16. The method of claim 15, whereinthe error correction scheme includes a turbo block code scheme.
 17. Amethod, comprising: encoding a message data stream with user data andfill data; modifying the fill data to reduce a chance of false messagedetection; encoding the message data stream with a parity check code incombination with an error correction scheme; creating a modified versionof the fill data in which the modified version fails a test for theparity check code; wherein the user data is unmodified to pass a paritytest and error correction test; and transmitting the message data streamfrom a transmission station.
 18. The method of claim 17, furthercomprising: creating a modified version of the fill data in which themodified version fails a test for the error correction scheme.
 19. Themethod of claim 17, wherein the fill data includes a pseudorandom binarysequence (PRBS).
 20. The method of claim 19, wherein the fill dataincludes a version of the PRBS modified by the parity check code and theerror correction scheme.
 21. The method of claim 19, wherein the paritycheck code includes a checksum.
 22. The method of claim 19, wherein theparity check code includes a cyclic redundancy check (CRC).
 23. Themethod of claim 19, wherein the error correction scheme includes forwarderror correction (FEC).
 24. The method of claim 17, further comprising:maintaining a signal lock on the message data stream through the filldata.
 25. A method, comprising: receiving a user data packet from a highspeed network at a transmission station; calculating a messagetransmission time for the user data packet across a primarycommunication channel; wherein the primary communication channel haslower bandwidth than the high speed network; wherein the transmissiontime across the primary communication channel is longer than across thehigh speed data network; calculating an inter-message transmission timebetween user data packets from the high speed network; determiningwhether to transmit the user data packet over the primary communicationchannel at least based on message transmission time and inter-messagetransmission time; accepting the user data packet for transmission overa primary communication channel when the message transmission timeacross the primary communication channel is more than an inter-messagetransmission time between user data packets; and transmitting a messageincluding the user data across the primary communication channel. 26.The method of claim 25, further comprising: rejecting the user datapacket for transmission over a primary communication channel when amessage transmission time is more than an inter-message transmissiontime.
 27. The method of claim 26, further comprising: transmitting amessage including the user data across a backend communication channel.28. The method of claim 25, wherein the user data packet concerns atransaction for a financial instrument.
 29. The method of claim 1,wherein the message has an integer number of modulated symbols.